Joseph Gwinn wrote:

[snip]
The Vigor furnace is rated at 1.6 KW, being 14 amps at 115 volts.
However, the heater coils are old, and only draw 11 amps at 113 volts,
or 1.24 KW. At full power (with no voltage drop in the controller),
after closing up a bunch of heat leaks, it gets to 1000 degrees C.

If I understand, you electronically control only one of the two banks,
the other being on or off as needed, so the electronic controller
handles 2 KW at 220 volts.

The controller controls all input to the kiln but if I don't need 4kW
then I just switch off one of the elements as they are in parallel.


OK. But this switching off is manual?



Yes, the energy controllers fitted to the kiln have an off position and
a full on position on the knob as well as settings in between.

I added a thermocouple to the kiln and connector into the box on the
side. The temperature controller is housed in a separate box with tails
out the back and mains plugs on the end so I can use it for controlling
other things if required, it also allows it to be placed away from the
heat. The thermocouple lead currently plugs into the front of the
controller box.

I thought of having a separate box, but all-in-one is more convenient,
and the commercial furnaces have the same scheme that I used, thermal
isolation using a set of parallel plates and spacers, so I knew it would
work.


I have a glass melting furnace in the build stages and that will have
its own controller permanently attached for convenience, the current
controller was built as a seperate unit so I can use it to control other
items if required.


What temperature does this require?

Depends on the glass but I intend to use one that would normally be
gathered at about 1100C, maximum intended glass temperature is 1250C and
element temperature will be a bit higher. Maximum for the likes of
Kanthal A1 is 1350C IIRC so pushing the upper limit but as I am
intending to be a glassblowing weekend warrior it's a workable and cheap
option compared to the likes of SiC or MoSi2 elements.



The finned heat sink is about 3"H x 3"W x 1.2"D and gets
warm to the touch when running max duty, like when firing to 1200C, but
very acceptable.


Operation at 220 volts cuts the current in half. A solid-state relay
(SSR) has a constant voltage drop, being 1.2 volts for the SSR I'm
using, so half the current is half the power to be dissipated in the
heatsink. This (and the distance from the furnace and its heat)
explains the difference in needed heatsink size.


Good point, I had failed to mention that I was running on 230V, the UK
standard mains voltage. I didn't occur to me that you were running yours
on 115V.


Yes, but we Yanks know where you live...

Joe Gwinn



One of these days I'll add a temperature controller I have to my small
Gallenkamp heat treatment furnace as the energy controller on that is a
pain, but the thermocouple read-out is accurate from checks I've done.


For the record, the old thermocouple that came with the Vigor is made of
14 guage chromel-alumel (Type K), appears to be original from 1979, and
reads about 5 degrees C low. It's still perfectly useable.

Joe Gwinn